Many devices are known in the art which provide means for supplying a pressurized gas, usually carbon dioxide, in a controlled manner for insufflating a patient during a surgical procedure. It is necessary to control both the flow rate and pressure of the insufflation gas during this process, in order to eliminate possible complications resulting from over pressurization of the patient's body cavity. Various methods for accurately determining the pressure within the patient's body cavity have been developed, some of which are described in the following U.S. Pat. Nos.:
5,013,294 (Bauer)
5,006,109 (Douglas et al)
4,874,362 (Wiest et al)
4,676,774 (Semm et al)
4,966,578 (Baler et al)
4,464,169 (Semm),
4,207,887 (Hiltebrandt)
All of the devices and methods known in the art are intended to provide a reasonably accurate indication of the actual pressure of the insufflation gas inside the patient's abdomen or other body cavity, and to cause additional insufflation gas to enter the patient's body if the actual pressure is less than the desired pressure.
During endoscopic surgery there are a number of external forces which may affect the pressure of the insufflation gas inside the body cavity including respiration by or mechanical ventilation of the patient, insertion and removal of tools and instruments from the body cavity and external forces applied to the patient's abdomen by the surgeon during the course of surgery. These external influences greatly affect the actual pressure in the body cavity.
It is desirable that an insufflation device be able to provide insufflation gas at a high flow rate, in order to quickly re-establish the correct pressure in the body cavity after insufflation gas is lost due to removal or insertion of a surgical instrument. Furthermore, it is recognized that an ideal insufflation device should be able to rapidly remove excess gas from the body cavity in the event that the pressure of the insufflating gas exceeds the desired level.
Insufflation devices known in the art will compensate for any decrease in the actual pressure in the body cavity by allowing additional gas to flow into the body cavity, but provide no means for allowing insufflation gas to be removed from the body cavity unless the actual pressure in the body cavity is much greater than the desired pressure. For example, although the insufflation pressure used for abdominal insufflation is typically 12 to 15 mmHg, the relief valve which is provided in most insufflating devices operates at 50 to 60 mmHg. In these devices, this relief valve is the only means provided by which the insufflating device can act to reduce the pressure of the insufflating gas in the patient's body cavity. Over pressurization is avoided by limiting the rate at which gas can flow from the insufflator into the body cavity, and by assuming that there will be gas leakage and absorption of gas within the body, both of which will tend to reduce the gas pressure. As these processes may remove gas at a lower rate than the insufflating device can supply replacement gas, there is a possibility that the actual pressure in the body cavity will exceed the desired pressure for extended periods of time.
Insufflating devices known in the art can not act to reduce the pressure in the body cavity due to the risk of cross contamination. If flow of gas out of the patient's body and into the insufflating device were permitted, bacterial and viral matter which may be present in the patient's body could be moved by the insufflation gas into the insufflating device, from where it can act as a source of infection to any patient with whom the insufflating device is subsequently used.
Contamination of the patient's body cavity can occur even if flow of gas back into the insufflating device is prevented. Recent studies (Douglas E. Ott, M.D., Georgia Biomedical Research Group, Macon, Ga.) have shown that insufflating gas provided by standard gas cylinders may be contaminated with both inorganic materials such as rust, copper, molybdenum and chromium, and with numerous organic contaminants, all of which could be introduced into the patient's body cavity during insufflation.
In summary, insufflation devices known in the art are not able to provide the high flow of insufflating gas which is desired by the endoscopic surgeon in part due to the lack of a means to relieve any over pressurization which may occur. Furthermore, any over pressurization which may occur as a result of patient respiration, external forces applied to the patient's body, manipulation of surgical instruments, or the operation of the insufflating device, may exist for long periods of time until leaks or absorption decrease the pressure of the insufflating gas in the body cavity. Pressure relieving means in existing insufflation devices are purposely set at a very high pressure in order to prevent flow of gas back into the insufflating device, which would cause cross-contamination and endanger patients. Existing insufflation devices also permit contaminants from the insufflation gas supply to enter the patient's body.